1. Field of the Invention
The present invention relates to image modification, and more particularly to image modification with the aid of a computer.
2. Description of the Related Art
In printing process, images are often modified by the technique called retouching. Retouching includes dot etching and color correction, which in the past have been a manual labor by a skilled operator. Recent developments in computer technology have enabled various image processors to execute image modification including the retouching by means of data processing.
Image modification process with the aid of a computer is described in International Patent Application PCT/DE80/00070 (or International Patent Laid-Open WO 80/02607), Japanese Laid-Open Gazette Hei-1-232482, and German Patent Application P3110222.0 (or Japanese Patent Laid-Open Gazette Sho-57-161858).
FIG. 1 is a view illustrating a color image I to be modified. The color image I is defined by four color signals representing concentrations of four colors Y (for yellow), M (for magenta), C (for cyan), and K (for black) in 256 gradations. In conventional automatic image modification, with the aid of an image processor, an operator specifies a subject region R to be modified with, for example, a digitizer and an electronic pen (or a stylus pen) on the color image I which is displayed on a color display.
Suppose an image of the Y (yellow) plate in the subject region R is processed by dot etching. Dot etching is image modification which changes a concentration level of pixels within a part of an image. As shown in FIG. 2, retouch coefficients K11 through Kmn each representing the intensity of a retouch effect (amount of dot etching) at each pixel in the subject region R are stored in advance in a coefficient table of the image processor. When the subject region R is specified by the operator, the retouch coefficients K11 through Kmn are added to the image data of the Y plate within the subject region. Here the subject region R includes m.times.n pixels, where m and n are integers and range from a few tens to several hundreds.
The intensity of the retouch effect usually depends on the position of a pixel in the image I. While observing the color display, the operator specifies the location of a subject region with a digitizer and changes the intensity of the retouch effect. Accordingly, the subject region of the image I is appropriately retouched.
In the conventional image processors described above, all retouch coefficients stored in a coefficient table (or in a memory) should be rewritten each time when the intensity of the retouch effect is changed. Such rewriting is laborious and time consuming; every time the operator changes the intensity of the retouch effect, the retouch process is interrupted by rewriting of the retouch coefficients in the coefficient table. This rewriting reduces the efficiency of the the image processors.